1. Field of the Invention
The present invention relates to a glass antenna device for mobile communication, and more particularly to a glass antenna device for mobile communication that can be installed on the window glass of a vehicle and can carry two different frequency bands.
2. Description of the Related Art
As an example of such an antenna, the assignee of the present invention has proposed a frequency switch type glass antenna in JP H6-291530A. This glass antenna includes a V-shaped radiation antenna pattern of differing length, and a grounding pattern arranged below that. A glass antenna in which the V-shaped radiation antenna pattern is made into a U-shape is disclosed as well. This glass antenna is specifically for car telephone transmission and reception in the 800 MHz band and the 1.5 GHz band. In this glass antenna, the core conductor of the coaxial cable that is arranged traversing the center of the grounding pattern is connected with the lower end of the V-shaped (or U-shaped) radiation antenna pattern.
In JP H8-162827A, the assignee of this invention has disclosed a glass antenna device for a car telephone. One feature of this glass antenna device for a car telephone is that it is provided with parallel impedance-adjusting portions running along the defogging heater conductors. The grounding pattern has a complicated shape.
In JP H7-297615A, the assignee of this invention has disclosed a window glass antenna device for a car. FIGS. 15 and 20 of that publication disclose a glass antenna that can carry two frequency bands.
In JP H6-276009A, JP H6-291531A, JP H6-303025A, JP H7-297615A, JP H8-139513A, JP H8-213820A and JP H9-321518A, the assignee of this invention has disclosed a glass antenna that can switch between the 800 MHz band and the 1.5 GHz band.
For suitable transmission and reception in different frequency bands with the glass antenna disclosed in JP H6-291530A, further improvements were necessary. That is to say, it was necessary to match the impedances adequately for the different frequency bands. In the glass antenna device disclosed in JP H8-162827A, on the other hand, a complicated conductive pattern was necessary, and parallel impedance adjusting portions were provided along the defogging heater conductors, so that there were problems with regard to the outward appearance. The glass antenna for car windows disclosed in JP H7-297615A can carry two frequency bands, but it needs two coaxial cables for that case.
It is thus an object of the present invention to provide a glass antenna device for mobile communication, in which impedance matching can be achieved for two frequency bands while preserving the features of the glass antenna disclosed in JP H6-291530A.
To attain these objects, a glass antenna device for mobile communication in accordance with the present invention includes an overall U-shaped antenna pattern, in which one end of a substantially straight first radiation antenna pattern and one end of a substantially straight second radiation antenna pattern are coupled by a coupling pattern that is substantially perpendicular to the first and second radiation antenna patterns. In this glass antenna device, the longitudinal direction of the coupling pattern is arranged substantially in parallel to the ground, and the length of the first radiation antenna pattern is different from the length of the second radiation antenna pattern.
Furthermore, a rectangular grounding pattern is arranged below the U-shaped antenna pattern. A core conductor of a coaxial cable is connected to the U-shaped antenna pattern, and a braided conductor of the coaxial cable is connected to the grounding pattern. An impedance-adjusting pattern is provided on a lateral portion of the grounding pattern.
The glass antenna device for mobile communication of the present invention uses a U-shaped antenna pattern, in which the ends of two radiation antenna patterns of different length are coupled, so that two different frequencies can be resonated. Therefore, it is not necessary to provide a shorting member or a switch or the like for switching frequencies. Furthermore, an impedance-adjusting pattern is provided at the grounding pattern, so that the glass antenna device of the present invention displays excellent transmission and reception characteristics in two different frequency bands.